A typical data storage system includes storage processing circuitry and an array of disk drives. The storage processing circuitry stores data into and retrieves data from the array of disk drives on behalf of external host computers. In some conventional data storage systems, the storage processing circuitry includes a Serial ATA interface (SATA) integrated circuit (IC) which communicates with the array of disk drives using the SATA protocol. The SATA IC enables the storage processing circuitry to operate as a SATA initiator by providing SATA commands to the array of disk drives. The array of disk drives operates as a set of SATA targets by responding to the SATA commands (e.g., by reading and writing data in response to the SATA commands).
One conventional data storage system includes two storage processors for high availability. Each storage processor includes a respective SATA IC having a send port and a receive port for each disk drive. Accordingly, if one storage processor fails, the other storage processor has access to each disk drive and can attempt to continue operation.
In the above-described conventional data storage system, each storage processor further includes a parallel bus device which is separate from the SATA IC of that storage processor. A direct memory access (DMA) engine of each storage processor then engages in DMA-based store and retrieve operations through the parallel bus devices to form a cache mirroring interface (CMI) path between the storage processors. As a result, each storage processor is capable of mirroring data in the cache of the other storage processor. With data mirrored in the caches, the storage processors are capable of operating in a write-back manner for improved response time (i.e., the storage processors are capable of committing to data storage operations as soon as the data is mirrored in both caches since the data remains available even if one storage processor fails).
Further details of various SATA specifications are available in a document entitled “Serial ATA II Electrical Specification,” Revision 1.0, May 26, 2004, the teachings of which are hereby incorporated by reference in their entirety.